U.S. patent number 5,123,417 [Application Number 07/555,985] was granted by the patent office on 1992-06-23 for apparatus and method for displaying ultrasonic data.
This patent grant is currently assigned to Diasonics, Inc.. Invention is credited to John Geis, Richard Lee, John Schultz, Quang Ton, Jack Walker.
United States Patent |
5,123,417 |
Walker , et al. |
June 23, 1992 |
Apparatus and method for displaying ultrasonic data
Abstract
The method of the present invention comprises displaying an
image comprising reflected pulsed doppler signals in real time
produced by reflecting a reference pulsed doppler signal, each
reflected signal displayed in a color defined by a polar coordinate
plot, wherein the polar coordinate plot comprises an origin
representing reflected signals of the reference pulsed doppler
signal having zero amplitude and zero frequency. The polar
coordinate plot further comprises an axis representing reflected
signals of the reference pulsed doppler signal having zero
frequency, a radius with respect to the origin representing
amplitude information of reflected signals of the reference pulsed
doppler signal, an angle with respect to the axis representing the
frequency of reflected signals of the reference pulsed doppler
signal, and a vector displaced 180 degrees from the axis, the
vector representing a Nyquist limit of the reference pulsed doppler
signal. The colors on the plot in a positive direction at a maximum
amplitude for a first frequency towards a point representing
maximum amplitude for a second frequency range from a first color
to a second color, colors on the plot in a negative direction at a
maximum amplitude for a third frequency towards a point for a
maximum amplitude for a fourth frequency range from a third color
to a fourth color, and the colors for each frequency on the plot
range from the color at a maximum amplitude for each frequency to a
fifth color at the origin.
Inventors: |
Walker; Jack (Sunnyvale,
CA), Ton; Quang (San Jose, CA), Geis; John (San Jose,
CA), Schultz; John (Santa Clara, CA), Lee; Richard
(San Jose, CA) |
Assignee: |
Diasonics, Inc. (Milpitas,
CA)
|
Family
ID: |
24219421 |
Appl.
No.: |
07/555,985 |
Filed: |
July 19, 1990 |
Current U.S.
Class: |
600/455; 348/163;
348/33 |
Current CPC
Class: |
G01S
15/8979 (20130101); G01S 7/52071 (20130101); A61B
8/463 (20130101); A61B 8/06 (20130101); A61B
8/08 (20130101); A61B 8/13 (20130101); A61B
8/488 (20130101) |
Current International
Class: |
G01S
15/89 (20060101); G01S 15/00 (20060101); G01S
7/52 (20060101); A61B 8/08 (20060101); A61B
8/06 (20060101); A61B 008/06 () |
Field of
Search: |
;358/81,82
;128/660.04-660.05,661.07-661.10 ;73/861.25 |
Other References
"Colour Flow Mapping Data Analysis . . . Linking the Vingmed CFM
With the Apple Mac II," Vingmed Sound, Interspec, 110 West Butler
Avenue, Ambler, PA 19002-5795 (undated)..
|
Primary Examiner: Jaworski; Francis
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor &
Zafman
Claims
What is claimed is:
1. A method of displaying reflected pulsed doppler signals in real
time produced by reflecting a reference pulsed doppler signal,
comprising the following steps:
a. displaying a first set of reflected signals in a first set of
colors specified by an ellipse wherein the frequency of each of the
first set of reflected signals with respect to the reference pulsed
doppler signal indicates relative motion towards an emitter of the
reference pulsed doppler signal, the amplitude for each of the
first set of reflected signals being a maximum, and each of the
first set of colors in the ellipse increases in brightness radially
around the ellipse in a first direction as the frequency of the
each of the first reflected signals increases, reaching a maximum
brightness at a first position on the ellipse, the first position
representing a Nyquist limit of the reference pulsed doppler
signal;
b. displaying a second set of reflected signals in a second set of
colors specified by the ellipse wherein the frequency of each of
the first set of reflected signals with respect to the reference
pulsed doppler signal indicates relative motion away from the
emitter of the reference pulsed doppler signal, the amplitude for
each of the first set of reflected signals being a maximum, and
each of the second set of colors in the ellipse increases in
brightness radially around the ellipse in a second direction as the
frequency of the each of the first reflected signals increases,
reaching a maximum brightness at the first position on the ellipse;
and displaying a third set of reflected signals in a third set of
colors, the third set of colors ranging from the colors for each of
the first set of signals and the second set of signals, to a
minimum saturation of the colors at the center of the ellipse.
2. A method of displaying an image comprising reflected doppler
display signals in real time produced by reflecting a reference
pulsed acoustic signal, each reflected doppler display signal being
displayed in a color defined by displaying a polar coordinate plot
comprising the following steps:
a. displaying an origin of the polar coordinate plot representing
reflected signals of the reference pulsed acoustic signal having
zero amplitude and zero frequency;
b. displaying an axis of the polar coordinate plot representing
reflected signals of the reference pulsed acoustic signal having
zero frequency;
c. displaying each color on the polar coordinate plot at a radius
with respect to the origin, the radius representing amplitude
information of reflected doppler display signals of the reference
pulsed acoustic signal;
d. displaying each color at an angle on the polar coordinate plot
with respect to the axis, the angle representing a frequency of
reflected signals of the reference pulsed acoustic signal; and
e. displaying a vector on the polar coordinate plot displaced 180
degrees from the axis, the vector representing a Nyquist limit of
the reference pulsed acoustic signal.
3. The method of claim 2 further comprising displaying colors on
the polar coordinate plot in a positive direction at a point
representing a maximum amplitude for first frequency towards a
point representing a maximum amplitude for a second frequency
ranging from a first color to a second color, colors on the plot in
a negative direction from a point representing a maximum amplitude
for a third frequency towards a point for a maximum amplitude for a
fourth frequency ranging from a third color to a fourth color, and
the colors for each frequency on the plot ranging from a color at a
maximum amplitude for each frequency to a fifth color at the
origin.
4. The method of claim 3 wherein the first color is red, the second
color is white, the third color is blue, the fourth color is white,
and the fifth color is black.
5. The method of claim 3 wherein the first frequency is zero, the
second frequency is the Nyquist limit, the third frequency is zero
and the fourth frequency is the Nyquist limit.
6. The method of claim 3 further comprising a user defining the
first, second, third, and fourth frequencies, and the first color
being displayed for all frequencies from the axis to the point
representing the first frequency at a maximum amplitude in a
positive direction, the second color being displayed for all
frequencies from the second frequency to the Nyquist limit at a
maximum amplitude in a positive direction, the third color being
displayed for all frequencies from the axis to the point
representing the third frequency at a maximum amplitude in a
negative direction, and the second color being displayed for all
frequencies from the fourth frequency to the Nyquist limit at a
maximum amplitude in a negative direction.
7. The method of claim 3 wherein the first, third and fifth colors
are black, and the second and fourth colors are magenta.
8. A method of displaying an image comprising reflected doppler
display signals in real time produced by reflecting a reference
pulsed acoustic signal, each reflected display signal being
displayed in a color defined by displaying a polar coordinate plot,
comprising the following steps:
a. displaying an origin of the polar coordinate plot representing
reflected signals of the reference pulsed acoustic signal having
maximum variance;
b. displaying an axis on the polar coordinate plot representing
reflected signals of the reference pulsed acoustic signal having
zero frequency
c. displaying each color on the polar coordinate plot at a radius
with respect to the origin, the radius representing variance
information of reflected signals of the reference pulsed acoustic
signal, wherein the maximum radius on the polar coordinate plot
represents reflected signals having minimum variance;
d. displaying each color on the polar coordinate plot at an angle
with respect to the axis, the angle representing a frequency of
reflected signals of the reference pulsed acoustic signal; and
displaying a vector on the polar coordinate plot displaced 180
degrees from the axis of the polar coordinate plot, the vector
representing a Nyquist limit of the reference pulsed acoustic
signal.
9. The method of claim 8 further comprising using colors on the
polar coordinate plot ranging from a first color for reflected
signals having a maximum variance, to a second color for reflected
signals having a minimum variance.
10. The method of claim 9 wherein the first color is green and the
second color is black.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of Doppler ultrasound
imaging in living tissue. Specifically, this invention relates to
an apparatus and method for display of ultrasonic data upon a video
display screen for observation and diagnosis by medical
personnel.
2. Prior Art
Images of living organisms typically utilize methods that pass
various types of radiation through the body of the animal and
measure the output with a suitable detector. For instance, x-ray
images are generated by producing x-rays external to the body,
passing the x-radiation through the body and observing shadows
produced on x-ray sensitive film. Ultrasonic images, in contrast,
are formed by producing ultrasonic waves using a transducer,
passing those waves through the body, and measuring the properties
of the scattered echoes from reflections inside the body using a
receptor. Ultrasonic imaging apparatus may be distinguished from
other medical imaging apparatus in the respect that they allow the
display of soft tissues within the body which show various
structural details such as organs and blood flow.
An ultrasonic imaging apparatus utilizes a probe which contains
elements for transmitting Doppler pulses throughout tissue. This
probe typically also contains receiving circuitry which allows
reception of the reflected Doppler pulses. Some of these probes
comprise a plurality of elements arranged in a linear fashion such
that each of the elements can be fired at various time intervals to
focus on specific parts of the body. In other systems, multiple
elements are simulated by means of a moveable mechanical element
within the probe wherein the Doppler pulses are transmitted at
various intervals along an axis, thus simulating a plurality of
elements in the probe. Each reflective pulse from the Doppler
pulses emitted may then be received by a receiving unit located in
the probe and transmitted to circuitry within the ultrasound
apparatus for processing and generation of a display. This display,
known as a b-mode image or two dimensional image of blood flow
velocity, may then be generated by the apparatus and displayed on a
video monitor for diagnosis and examination by an attending
operator or physician.
The basic principle used in applying the Doppler method for
ultrasonic imaging in a pulsed Doppler ultrasound apparatus is
described as follows. When blood flow within a living subject is
subjected to ultrasonic waves, corpuscles are caused to vibrate
slightly while moving and reflect those ultrasonic waves. Because
of the velocity of the corpuscles the frequency of the reflected
waves changes from that of the transmitted waves due to the Doppler
effect. The frequency shift may be detected and the amount of the
shift may be displayed on a video screen for imaging blood flow in
the living subject. Since the amount of shift of the transmitted
waves is in relation to the blood flow velocity, the amount of
blood flow and the speed of the blood flow may be observed. Noise
and other signals (clutter) which have Doppler shift but don't
represent blood movement in the body are filtered out. The image
produced will then only represent that which is in motion. This
Doppler shift frequency information is then used as blood flow
information for forming a two-dimensional image or profile of the
blood flow velocity.
One such apparatus used in displaying information obtained from
ultrasonic pulses transmitted in the human body is shown in FIG. 1
as imaging system 100. Imaging system 100 generally comprises a
probe 101 which is coupled via line 110 to transmitter/receiver
circuitry 102. Transmitter/receiver circuitry 102 is designed so
that the elements in probe 101 will be fired at specified time
intervals, with reflective pulses being detected using probe 101 at
another given time interval. Transmitter/receiver circuitry 102 is
coupled to a control unit 109 via bus 120. Control unit 109
controls all circuitry in the imaging system via bus 120. Control
unit 109 is further coupled to a keyboard 125 and a mouse,
trackball or other device 126 for movement and control of
information shown on video display 130.
Once a pulse is received by transmitter/receiver 102, such
information is transmitted by line 111 to RF (radio frequency)
processor 103 for further processing. This radio frequency
information is further transmitted via line 114 to a graphic
processor 105 and to a Doppler processor 106 via lines 114 and 113
for generation of black and white ultrasound information on video
display 130. Information generated by Doppler processor 106 via
in-phase (I) and quadrature (Q) signals output from RF processor
103 are transmitted via line 115 to graphics processor 105.
Graphics processor 105 then integrates information received from RF
processor 103 and Doppler processor 106 and then transmits scan
line information to video processor 108 via line 116. In addition
to information passed to graphics processor 105 and Doppler
processor 106, RF processor 103 transmits I and Q signals via line
112 to color flow processor 104. Color flow processor 104 is also
controlled by control unit 109 via bus 120. Color flow processor
104 is used for detecting Doppler shift and blood flow information
in living tissue, and thus transmits this information via line 117
to a color scan converter 108. Such color information is used to
graphically represent on video display 130 moving blood flow in a
living organism. The color scan converter is used to interpolate
point scan line information obtained from color flow processor 104,
and transmit that information on line 118 to video processor 120
for representation of color blood flow in the human body. Video
processor 120 then utilizes information obtained from graphics
processor 105 for display of black and white ultrasound information
and color information obtained from color scan converter 108 to
generate color ultrasound information suitable for output on a
video display such as 130 via line 119. Such information may be
transmitted in National Television Standards Committee (NTSC)
format and thus be stored on video tape for later clinical
examination by attending medical personnel.
A prior art display of color Doppler ultrasound information is
shown in FIG. 2 as screen 300. Screen 300 comprises a scan area 301
wherein portion 305 of scan area 301 is represented in various
colors. The remainder of 301 outside 305 shows black and white
ultrasound information caused by relatively stationary tissue
and/or blood flow in the body being imaged. The Doppler color flow
information in area 305 is shown in colors represented on scale 310
shown on the right hand portion of screen 300. One axis 321 of
scale 310 represents frequency, and the second axis 320 on scale
310 represents amplitude. The range of amplitude and frequency of
each pulse is represented form zero to the maximum detectable
amplitude by the ultrasound receiver of probe 101 in ultrasound
system 100. Frequency information is determined by measuring the
phase shift of reflected waves from the pulse repetition frequency
(PRF) of the reference wave. This is done, in a manner known in the
art, by determining phase shift from the PRF and direction of phase
shift from the PRF using I and Q signals obtained from the
reflected Doppler pulses.
The frequency information shown on scale 310 will be displayed as
various colors on scan region 301 according to the colors shown in
scale 310. For instance, an area shown as 304 in scan area 301 may
be represented in a color defined on scale 310 as 311. This area
311 may correspond with certain amplitude and frequency ranges for
the reflected Doppler pulses. Likewise, other colors may further be
represented on scale 310 and correspond with areas shown in scan
area 305. For instance, area 304 may be represented in a color
defined as being within the frequency and amplitude range shown on
scale 310 as 312, and area 302 may be within the frequency and
amplitude ranges shown on scale 310 as area 313. In this manner of
the prior art shown as screen 300 in FIG. 2, speed and amount of
blood flow information in a living organism may be clearly shown on
a two-dimensional video display screen 130 for analysis.
One additional feature of the prior art system is that certain
blood flow may be represented as moving towards probe transducer
101 shown in FIG. 1, and other blood flow will be shown as
traveling away from probe 101 depending on the scale displayed as
310 of screen 300. For instance, one point on scale 310 such as
325, may be an origin representing blood flow with zero phase shift
(zero velocity). Any regions shown in a color represented in area
326 of scale 310 may be represented as going away from the
transducer, and areas shown in colors represented in area 327 may
be represented as traveling towards the transducer. These colors,
of course, are dependent upon whether the frequencies show a
positive or negative Doppler shift from the PRF.
The choosing of a PRF is dependent upon the depth of the scan being
performed, and the amount of frequency resolution required by the
operator. For instance, the greater the PRF, the greater the amount
of frequency resolution in the color-flow image, however, the
shallower the depth of the scan. In a typical ultrasonic imaging
system, each color sample volume (CSV--a horizontal row on a
display), may range from approximately 0.5 millimeters to one
centimeter. One aspect of the PRF is that motion of extremely high
rates towards or away from the transducer generates reflected
Doppler signals which are incorrectly represented on screen 300.
These reflected Doppler signals may appear to be in motion away
from the transducer when the blood flow is actually towards the
transducer. These errors generally occur when the phase shift from
the PRF is greater than 180 degrees, or the reflected signal is
greater than PRF/2 (or less than-PRF/2 is the negative direction).
Generally, the PRF must be twice that of the maximum frequency
expected to be received to prevent this error from occurring. If
the frequency of the reflected wave is greater than PRF/2, then the
reflected Doppler wave will be assigned to an erroneous frequency.
This error in assignment is called aliasing, and the frequencies at
which aliasing occurs (.+-.PRF/2) are known as the Nyquist limits.
The Nyquist limits of the prior art system shown on screen 300 of
FIG. 2 are represented as points 314 and 315. If point 315 is the
positive Nyquist limit and 314 is the negative Nyquist limit for
the PRF, certain reflected pulses which exceed the frequency 315 on
scale 310 will appear in area 326 (the negative area) of scale 310.
Although the Nyquist limit of the PRF is an inherent limitation in
pulsed Doppler systems, the prior art color display shown as screen
300 in FIG. 2 does not clearly illustrate this aliasing error.
Therefore, an improved method for displaying colors in an
ultrasonic pulse Doppler imaging system is required which will
clearly display the aliasing error. This allows an operator
performing the scan to adjust the PRF, if desired, to minimize
aliasing problems and maximize the resolution of displayed
information.
SUMMARY AND OBJECTS OF THE INVENTION
One object of the present invention is to provide color display of
ultrasonic information in real-time in such a way as to clearly
show aliasing errors from a reference Doppler pulse, to allow
diagnostic personnel to minimize such errors while maintaining
effective diagnostic resolution of diseased tissue and blood
flow.
Another object of the present invention is to provide alternative
displays of ultrasound data in a manner which assists the viewing
of certain conditions.
These and other objects of the present invention are provided for
by a method of displaying an image comprising reflected pulsed
Doppler signals in real time produced by reflecting a reference
pulsed doppler signal, each reflected signal displayed in a color
defined by a polar coordinate plot, wherein the polar coordinate
plot comprises an origin representing a reflected signals of the
reference pulsed doppler signal having zero amplitude and zero
frequency. The polar coordinate plot further comprises an axis
representing reflected signals of the reference pulsed doppler
signal having zero frequency, a radius with respect to the origin
representing amplitude information of reflected signals of the
reference pulsed doppler signal, an angle with respect to the axis
representing the frequency of reflected signals of the reference
pulsed doppler signal, and a vector displaced 180 degrees from the
axis, the vector representing a Nyquist limit of the reference
pulsed doppler signal. The colors on the plot in a positive
direction at a maximum amplitude for a first frequency towards a
point representing maximum amplitude for a second frequency range
from red to white, colors on the plot in a negative direction at a
maximum amplitude for a third frequency towards a point for a
maximum amplitude for a fourth frequency range from blue to white,
and the colors for each frequency on the plot range from the color
at a maximum amplitude for each frequency to black at the
origin.
These and other objects are provided for by a method for displaying
an image comprising reflected pulsed doppler signals in real time
produced by reflecting a reference pulsed doppler signal, each
reflected signal displayed in a color defined by a polar coordinate
plot. The polar coordinate plot comprises an origin representing
reflected signals of the reference pulsed doppler signal having
maximum variance and an axis representing reflected signals of the
reference pulsed doppler signal having zero frequency. The polar
coordinate plot further comprises a radius of each color with
respect to the origin representing variance information of
reflected signals of the reference pulsed doppler signal, wherein
the maximum radius represents reflected signals having minimum
variance, and the angle of each color on the polar coordinate plot
with respect to the axis representing a frequency of reflected
signals of the reference pulsed doppler signal. Also, the polar
coordinate plot comprises a vector displaced 180 degrees from the
axis, wherein the vector representing a Nyquist limit of the
reference pulsed doppler signal. The ultrasonic information is
displayed in shades of green wherein green represents maximum
variance information and black represents minimum variance
information according to the polar coordinate plot.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not
limitation in the Figures of the accompanying drawings in which
like references indicates similar elements and in which:
FIG. 1 shows a prior art ultrasonic imaging system.
FIG. 2 shows a prior art color display of ultrasonic imaging data
used to represent reflected Doppler pulses.
FIG. 3 shows a red/blue color Doppler display of blood flow used in
the preferred embodiment along with a color wheel map.
FIGS. 4A and 4B show how the color wheel of the preferred
embodiment may correspond with a color scale used in a prior art
ultrasonic imaging apparatus.
FIG. 5 shows the distribution of colors in color wheel of the
preferred embodiment.
FIGS. 6-9 show the steps used in remapping the frequency range of
the color wheel of the preferred embodiment.
FIG. 10 shows an amplitude-only display of ultrasonic images with a
color wheel map.
FIGS. 11A and 11B show spectral traces of reflected Doppler pulses
versus time, one display with low variance and the other with high
variance.
FIG. 12 shows how variance information may be represented in a
blood flow display using the color wheel of the preferred
embodiment.
DETAILED DESCRIPTION
The present invention covers a method and apparatus for acquiring
ultrasonic imaging data, and displaying that data on a suitable
video display screen. In the following description, numerous
specific details are set forth such as colors used, specific
hardware components, etc., in order to provide a thorough
understanding of the present invention. It will be obvious,
however, to one skilled in the art that these specific details may
not be required to practice the instant invention. In other
instances, well-known components of ultrasonic imaging apparatus
have not been described in detail to not unnecessarily obscure the
present invention.
Referring to FIG. 3, ultrasonic information obtained from color
flow processor 104 and color scan converter 108 via line 118, is
displayed by video processor 120 in the preferred embodiment as
image 600 on video display 130. As shown on video display 600 of
FIG. 3, a region of interest 610 may be selected by an operator for
the display of color ultrasound information. Generally, ultrasound
information outside region of interest 610 on screen 600 is shown
in a gray scale format. Generally, those objects inside region of
interest 610 which are not moving or are moving at a very slow rate
and thus have very little detectable phase shift from the PRF will
also be displayed in gray scale. As shown in region of interest
610, a blood vessel such as 620 may be displayed in color. Each of
the shaded areas shown in 610 are displayed in color and are
representative of certain frequency phase shifts from the PRF for
screen 600.
Notice that screen display 601 further comprises a color wheel 650
which contains certain colors corresponding with colors displayed
in region of interest 610. Color wheel 650 is a polar coordinate
plot containing colors for certain frequency and amplitude ranges.
The angle of each vector on color wheel 650 represents, in the
preferred embodiment, frequency (velocity) for reflected signals.
The radius of each color on color wheel 650 represents amplitude
information (strength of signal) for reflected signals. For each
color displayed in region of interest 610, the same color is shown
on color wheel 650. The frequency and amplitude of the reflected
wave in region of interest 610 can be determined by referring to
the position of the color on color wheel 650. In the preferred
embodiment, color wheel 650 is elliptical in shape, however, any
somewhat circular shape may be used for color wheel 650 in
alternative embodiments. As shown on FIG. 3, region 611 is
represented in a color shown on color wheel 650 as 661. Likewise,
regions 612 are represented in a color shown in region 662 on color
wheel 650, and region 613 on display 600 is shown in a color
represented on color wheel 650 as 660. Finally, region 614 on
display 600 is shown on color wheel 650 as 663.
Note that each color on color wheel 650 represents a specific
frequency and amplitude for a reflected signal shifted from the
PRF. Colors on the right side of color wheel 650 in the preferred
embodiment are shown in shades of red, and are represented as
frequencies red-shifted from the PRF (indicating motion towards
probe 101). This is indicated by the vertical arrow 690 pointing
upwards as shown on display 601. Conversely, colors such as 663
which are on the left side of color wheel 650 are represented in
shades of blue. These are frequencies that are blue-shifted from
the PRF (indicate motion away from probe 101). This is indicated by
vertical arrow 680 pointing downwards. A more detailed description
of the color wheel's mapping for a display such as on screen 600 is
discussed with reference to FIGS. 4A and 4B.
The mapping of colors to frequencies and amplitudes on color wheel
650 is shown in more detail and discussed with reference to FIGS.
4A and 4B. Shown in FIG. 4B is a prior art color scale 700 which is
similar to scale 310 of FIG. 2. As shown in 650 of FIG. 3, a given
series of colors, such as those used to represent region of
interest 610 in FIG. 3, may be mapped to a polar coordinate scale.
650 may correspond with certain frequencies and amplitudes shown on
a prior art scale such 700. In the preferred embodiment, the angle
of a vector intersecting a color, such as 600, represents the
frequency of a reflected wave which has been shifted from the PRF.
The shift of the reflected wave is positive if the color lies
between points 710 and 720 in direction 740 on wheel 650, or is
negative if it lies between points 710 and 720 in direction
750.
The radius of the position of the color for color wheel 650
represents the amplitude of the reflected wave. Small amplitudes
are represented by colors residing at small radii in color wheel
650 (with origin radius 711 having zero amplitude) and colors
indicating larger amplitudes residing at larger radii. As shown in
FIG. 3, an area such as 613 which is displayed in the color
represented in region 660 of color wheel 650, has a certain
frequency and amplitude as determined by the color's location on
color wheel 650. The same color may be represented on a prior art
map such as 700 wherein a horizontal axis such as 771 represents
frequency information, and a vertical axis such as 772 represents
amplitude information. As mentioned above, each color on color
wheel 650 shown from point 730 to point 733 in direction 740 is
represented in a shade of red since it represents frequencies that
are red-shifted from the PRF. Conversely, colors on color wheel 650
between points 731 to 732 in direction 750 are shown in shades of
blue representing blue-shifted frequencies from the PRF.
Also shown on color wheel 650 is origin 711 and origin vector 710
which represent the extreme low amplitude and low frequency ranges
for the colors of reflected pulses, respectively. Below certain
frequency phase-shifts such as minimum frequencies 730 and 731 on
scale 650, information that is received generally tends to be
clutter (noise or stationary objects) so it is filtered out. Any
phase shifts detected below 730 and 731 are not displayed and are
instead represented in black in region 710 (an origin vector) on
color wheel 650. Likewise, no meaningful amplitude information is
available below a certain amplitude. As shown in region 711, black
(no color) is used to represent signals having amplitudes less than
a given level. The amplitude information in this area for certain
reflective pulses is generally clutter.
As discussed above, very fast motion of blood may generate aliasing
errors. In other words, some blood flow may be shown as moving the
opposite direction than it is actually moving. Aliasing errors will
tend to be large for small PRFs and will decrease for larger PRFs.
The larger the PRF, however, the less the resolution of the
resulting display. As shown in prior art scale 700, an extremely
fast blood flow such as that shown in region 614 of FIG. 3, may
erroneously be represented as an extremely blue-shifted blood flow.
This region's frequency is shown in a color represented in area 763
of scale 700 shown in FIG. 4B. It is known that blood flow in the
center of an artery such as 620 in FIG. 3 has a higher velocity
than the blood flow at the edges. So, the operator of ultrasound
imaging apparatus 100, when viewing the image shown in 600 of FIG.
3, may realize that region 614 is in fact a very fast blood flow
that is causing aliasing. Corrective measures may then be taken
such as increasing the PRF, thus showing region 614 as a properly
red-shifted display. However, when using a scale such as 700 in
FIG. 4B, this aliasing error will not be clearly illustrated since
the color will be represented as having a negative phase shift,
such as shown in area 763, when in fact it is probably a very large
positive phase shift. Color wheel 650 can actually be viewed as a
flat scale such as 700 wrapped upon itself (where positive and
negative Nyquist limits 760 and 770 are touching). Color wheel 650,
in contrast to prior art scale 700, will have only one Nyquist
limit vector 720 (.+-.PRF/2). Aliasing can be clearly observed on
color wheel 650 by noting colors that are represented clockwise
(for a negative aliased phase shift) or counterclockwise (for a
positive aliased phase shift). If aliasing is suspected it may be
confirmed by reference to color wheel 650.
For instance, if given blood represented in a color such as 761 on
scale 700, when the blood is accelerated to a velocity causing a
phase shift just beyond Nyquist limit 720, then the same blood flow
for the same amplitude would be represented as extremely
blue-shifted blood flow on scale 700 in the color shown as 763.
Color wheel 650 clearly illustrates this type of aliasing error.
For instance, as shown in FIG. 3, the blood flow shown in area 614
of display 600 corresponds with the color shown in region 663 of
color wheel 650 in FIGS. 3 and 4A. This color is probably a faster
moving blood flow than that shown in regions 612 of screen 600
because region 614 is in the center of the artery and it is known
that blood flows faster in the center of an artery than at the
sides such as shown in areas 612. The operator can then readjust
the PRF to clearly show region 614 in a color indicating red shift.
Alternatively, the operator might merely take note that region 614
is extremely fast moving blood flow which generates frequencies
beyond the Nyquist limit. The advantage of the preferred
embodiment's method of representing color data is that the positive
and negative Nyquist limits intersect. Thus, the aliasing error
that occurs at Nyquist limit 720 on color wheel 650 is clearly
illustrated by a color counterclockwise from the Nyquist limit when
the limit is exceeded by a fast velocity in the positive direction.
Likewise, a negative velocity generating a frequency below the
negative Nyquist limit may be clearly illustrated in a color
clockwise from Nyquist vector 720. In contrast, the aliasing
occurring at positive and negative Nyquist limits 760 and 770 on
prior art scale 700 is obscured since it is not clear whether the
frequency shown is actually a negative phase shift, or an extremely
fast moving blood flow generating a positive phase shift. It can be
appreciated that the preferred emboidment's representation of
colors in this circular fashion conveys more information than the
prior art system.
To clearly illustrate the red and blue shifting from the PRF on
display 601, colors are represented on color wheel 650 in
counterclockwise direction 740 from 730 to Nyquist limit 720 in
shades of red. In the preferred embodiment, the maximum amplitude
at the frequency just before the Nyquist limit (points 733), the
color will be the minimum saturation and maximum luminance value
(white). Wheel 650's color will range from this color to the
maximum saturation of red at point 730. Intermediate colors for the
maximum amplitude around color wheel 650 in direction 740 will be
represented as shades of red between those two values. Conversely,
in direction 750 (representing blue-shifting) from point 731 to
point 732 (at the maximum amplitude), the color will range from
maximum saturation for blue at point 731 to maximum luminance and
minimum saturation at point 732 (white). Further, as the amplitude
decreases on color wheel 650 (the radius decreases), the luminance
of the color decreases. Luminance and saturation are a minimum at
origin 711 and origin vector 710. In summary, on color wheel 650,
luminance is a function of amplitude and saturation is a function
of frequency. Luminance is a maximum at Nyquist vector 720 for the
maximum amplitude. Saturation is a maximum at a point just beyond
the origin vector 710 (points 730 and 731), and a minimum at the
Nyquist limit vector 720. It can be appreciated from the foregoing
that many colors may therefore represent the frequency and
amplitude range of imaging system 100. A unique color may therefore
be generated for each frequency and amplitude displayable on color
wheel 650. Since each color on a display such as 600 of FIG. 3,
corresponds with a certain frequency and amplitude range, in the
preferred embodiment, the frequency and amplitude of each signal
may be determined by referring to the same color on color wheel
650.
Because the sensitivity of system 100 increases as the amplitude
(strength) of the Doppler signal increases, the number of colors in
the preferred embodiment representing each frequency at each
amplitude can also increase on color wheel 650 to show more
information. FIG. 5 shows the actual number of colors present on
color wheel 650 in the preferred embodiment. Once the amplitude
reaches a certain minimum value, those amplitudes are represented
in a certain number of colors. For instance, at radius 830 (the
minimum amplitude displayable in color) shown in FIG. 5, the
frequencies for reflected pulses are represented in two colors
only. Therefore, reflective pulses having a minimum amplitude
defined by ring 830 and any red-shift (region 831) will be
represented in one shade of red. Conversely, any reflective pulses
having blue-shifting at amplitude 830 (region 832), will be
represented in one shade of blue. The maximum displayable
amplitude, such as that represented at ring 800 of color wheel 650,
will be represented in 32 colors (16 for the range of the
blue-shifted frequencies, and 16 for the range of the red-shifted
frequencies, respectively). Each ring towards the center
progressively has fewer colors which may represent the frequencies
at the amplitude. For instance, at the amplitude represented at
ring 810, only 30 colors are represented (15 for red and
blue-shifted frequencies, respectively). At amplitude represented
by ring 820, 24 colors are present (12 for red and blue-shifted
frequencies, respectively), at ring 840 18 colors are present (9
for red and blue-shifted frequencies, respectively), 12 for those
frequencies at the amplitude represented by ring 850 (6 for red and
blue-shifted frequencies, respectively), and for frequencies
represented at the amplitude represented by ring 860 of color 650,
there are only 6 colors present (3 for red and blue-shifted
frequencies, respectively). Thus, there are a total of 122 colors
available for display on an ultrasonic image on video display
130.
OPTIMIZING COLORS
The 122 color range on color wheel 650 may also be optimized
(re-mapped) for certain frequencies shown in fewer colors on
display 600. This will enhance the detail for certain frequency
ranges that the operator of ultrasonic imaging apparatus 100 finds
interesting. For instance, as shown in FIG. 6, a new region of
interest 970 may be displayed on screen 600. Region 970 shows a
portion of blood vessel 915 and has an area 930 which is
represented in only one color shown corresponding with the
amplitudes and frequencies for the area 931 shown on color wheel
650. Area 930 may be viewed as interesting and a clinician may
desire to enhance the detail within that region. In order to
enhance the detail, a remapping of the color range for the
frequencies contained within area 930 for color wheel 650 may be
performed which will show region 930 with more than one color. This
optimization is shown and discussed with reference to FIGS. 6
through 9.
The first step in remapping the frequencies vs. colors for area 930
is shown in FIG. 6. First, the user will indicate to system 100
that color optimization of wheel 650 is required. This is done by
depressing, in the preferred embodiment, an appropriate key on
keyboard 125 of system 100 shown in FIG. 1. As shown in FIG. 6,
mapping display 900 will appear showing a color vs. frequency
graph. Curve 910 represents the current frequency vs. color mapping
used on color wheel 650. Horizontal axis 901 represents the
currently displayable frequency range (0 to PRF/2), and the
vertical axis 902 represents the current color range. Message 950
indicates that once the user depresses the "Enter" key on keyboard
125, color optimization will start. Once the "Enter" key is
depressed, the display will change to correspond with that shown in
FIG. 7.
The next step in the color optimization process is shown in FIG. 7.
Once color optimization is started, message 1050 is displayed on
video display 130. 1050 requests entry of the minimum frequency on
color wheel 650 for the new color range. Once selected, display 900
now indicates at point 1001 the minimum frequency at which the
maximum saturated color will be displayed. This is the point where
the colors will begin to be distinguished on color wheel 650. The
minimum frequency will be adjustable by moving an input device, in
the preferred embodiment such as a trackball or mouse 126 shown in
FIG. 1, in the horizontal directions 1020 and 1021 on display 900
to move minimum frequency 1001 as shown in FIG. 7. As trackball 126
is moved and point 1001 of 900 moves in directions 1020 and 1021,
vectors 1031 and 1041 will move radially about color wheel 650 to
correspond with the positive and negative values of the minimum
frequency 1001 currently selected. For instance, if the frequency
1000 Hz was represented at 1001, then the color from origin vector
710 on color wheel 650 to vector 1031 (representing 1000 Hz) would
be represented in only one color, the maximum saturation of red
(region 1030). Likewise region 1040 from origin vector 710 to
vector 1041 (-1000 Hz) on color wheel 650, would be represented in
the maximum saturation of blue.
Once the minimum frequency has been determined, the user of system
100 must determine the maximum frequency range for which the color
range is to be mapped. This step is shown in FIG. 8. Message 1150
prompts the user to locate the maximum frequency for color wheel
650 on display 900 for which the color range is going to be mapped.
Note minimum frequency 1001 is now shown as a vertical dashed line
on display 900. Notice also that there is a second point 1101 of
curve 1100 for which the maximum frequency of the 122 possible
colors is represented. As with minimum frequency 1001, trackball
126 may used to move maximum frequency 1101 horizontally in
directions 1120 and 1121 to define the maximum frequency
displayable. As this is done, vectors 1141 and 1131 move radially
in directions 1135 around color wheel 650 such that areas 1140 and
1130 become larger and smaller depending on maximum frequency 1101.
Note that as the frequency range for maximum frequency 1101
encompasses the frequencies currently represented in region 930,
region 930 will change to the color shown in region 1130 on color
wheel 950. Once maximum frequency 1101 has been defined, the user
then depresses the "Enter" key on keyboard 125 in the preferred
embodiment. System 100 then remaps the displayable color range to
the frequencies indicated as the minimum and maximum. In addition,
the color values for the range are recalculated (optimized) for
this new frequency range between minimum frequency 1001 and maximum
frequency 1101.
Once the color range is remapped, as shown in 900 of FIG. 9, curve
1200 now represents the current frequency vs. color mapping which
is displayed on color wheel 650. Message 950 again prompts the user
to redefine color wheel 650, if desired. Note that the minimum
frequency for the maximum saturation and luminance of the colors is
now shown as 1001 as in the earlier figures, and the maximum
frequency representing the minimum saturation for each color is now
represented at point 1101 as shown on display 900 of FIG. 9.
Between vectors 1231 and 1232 in the positive direction the full
red color range is mapped. Also between vectors 1241 and 1242 in
the negative direction, the full blue color range is mapped. As a
result of this optimization, the detail within the feature 930 on
display 600 has now been enhanced. For instance, area 1250 is now
represented in a color shown by the frequency and amplitude in
region 1230, or an area below the new color mapping range (vector
1001). Area 1251 on display 600 is now represented in a color shown
on color wheel 650 as 1233, and area 1252 is represented in a color
represented in an area 1234 of color wheel 650. As a result of the
foregoing operation, the detail in region 930 has now been
enhanced. This provides more information to an attending physician
for diagnosis of diseased tissue which may be present and indicated
by the blood flow shown in area 930.
AMPLITUDE-ONLY DISPLAY
Referring to FIG. 10, an alternative embodiment of the present
invention is shown wherein color wheel 1300 represents
amplitude-only information. All of the colors in color wheel 1300
are now represented in shades of magenta, instead of red and blue.
Positive and negative phase shift information has been eliminated.
In display 600 shown in FIG. 10, each of the colors in region of
interest 1310 are represented in various shades of magenta
according to amplitude-only color wheel 1300. Color wheel 1300,
like color wheel 650, represents frequency information as the angle
of the vector offset from the origin vector 1301. Also, each radius
extending out from a center 1302 represents amplitude information.
There is an increase in luminance in both directions 1310 and 1320
from origin vector 1301 until the maximum luminance for magenta is
reached at the outer ring at Nyquist limit vector 1305. In
addition, luminance is a function of amplitude and ranges from a
minimum at central origin 1302 to the maximum luminance for a given
frequency at the outer ring, such as Nyquist limit vector 1305.
As can be appreciated from color wheel 1300, the two halves 1330
and 1340 of color wheel 1300 are also symmetric with respect to one
another. That is, a given shade of magenta will be represented as
the same shade as magenta on the opposite side of color wheel 1300.
Region of interest 1310 then will display colors corresponding with
color wheel 1300 without showing positive or negative Doppler shift
information. For instance, areas 1352 and 1353 may be represented
in colors shown on color wheel 1300 at positions 1313 and 1314.
Area 1351 may be represented in the color shown at areas 1311 and
1312. Further, areas 1354 may have a specific amplitude represented
on color wheel 1300 at positions 1308 and 1309. The amplitude-only
display shown as screen 1380 in FIG. 10 may have a specific
clinical application such as representing the efficiency of a heart
pumping certain volumes of blood through a blood vessel. A display
like that enclosed within the region of interest 1310 on display
600 may be generated to show this information without red or blue
shift information. In the preferred embodiment, the shades of color
represented in wheel 1300 are magenta, but in alternative
embodiments, the color may vary accordingly.
VARIANCE-ONLY COLOR DISPLAY
Additionally, color wheel 650 may be used to represent variance
information in a given blood flow. Variance is represented as the
difference between a signal having the lowest velocity (phase
shift) and a signal at the same point having the highest velocity
(phase shift). As shown in FIGS. 11A and 11B, examples of low
variance and high variance are shown. 1400 of FIGS. 11A and 1450 of
FIG. 11B are representative of spectral traces of velocities over
time. The horizontal axes 1401 of 11A and 1451 of 11B represent
time and the vertical axes 1402 and 1452 represent frequency phase
shifts from the PRF. Each of the curves 1400 and 1450 represent
blood flow in a living organism. The curves show blood flow
according to heart beats at one location. As is shown in 1400 of
FIG. 11A, at a given point 1407 two particular points 1405 and 1406
may represent signals having a maximum velocity and minimum
velocity for blood flow at a particular time for the area. Such a
display as 1400 will show a narrow bandwidth for blood flow, or low
turbulence, and therefore a low variance. In contrast, for a given
time 1457, display 1450 of 11B will have a given maximum frequency
1455, and a minimum frequency 1456 at time 1457. The difference
between maximum frequency 1455 and minimum frequency 1456 is much
greater than that in 1400 for the region. Curve 1450 therefore has
a higher bandwidth, or a higher turbulence and therefore a higher
variance than the curve given in 1400. This turbulence or high
bandwidth information may indicate disease or an obstruction in a
blood vessel. This information is displayed independent of a
standard red/blue or amplitude-only Doppler display as shown in
earlier figures.
Referring to FIG. 12, 1501 shows an example of a variance-only
Doppler display. Display 600 now shows a region of interest 1500
which contains a blood vessel 1571 showing variance information
according to color wheel 1500. Color wheel 1500 will map color in a
manner reversed from the amplitude-only and the red/blue Doppler
shift displays. That is, radius information in color wheel 1500
will represent degrees of variance, however, origin 1501 will
represent the greatest amount of variance displayable. The angle of
a vector at a particular point will represent the average frequency
for the Doppler shifted signals at that point. The color mapping is
accomplished wherein the higher variance values shown at the center
are represented in a maximum saturation of green and the lower
variance values are represented on color wheel 1500 with lower
saturation and luminance values. The outer-most rings of the color
1500 such as 1505 will be represented in black (no saturation or
luminance and therefore no variance). For instance, with reference
to region of interest 1550 in FIG. 12, showing variance in blood
vessel 1571, region 1573 may have high variance values represented
in a color which corresponds with area 1501 on color wheel 1500.
Regions 1574 may correspond with a color shown in area 1504 (lower
variance) on color wheel 1500, regions 1575 may have variance
values associated with the color shown at area 1503 in color wheel
1500 (even lower variance) and 1572 may correspond with the color
area 1502 (very low variance). The variance shown in blood vessel
1571 may be caused by an obstruction or blockage on blood vessel
1571 such as 1570 which may be caused by disease. Therefore, this
type of variance display is useful for some types of clinical
applications. Since the variance information is shown in a manner
inverted from that of the amplitude-only and the red/blue displays
discussed above, a variance display such as shown in FIG. 12 may be
displayed simultaneously with an amplitude-only and a red/blue
display as shown in FIGS. 6-14. This type of display may provide a
rich amount of data, indicating blood flow velocity and amplitude,
as well as variance information according to a display such as that
shown in FIG. 12.
As discussed above, the circular fashion in which the color coding
has been mapped in the preferred embodiment for the red/blue,
amplitude-only and variance displays is a vast improvement over the
prior art's rectangular coordinate system because it clearly shows
the aliasing effect of an ultrasonic pulsed Doppler imaging system,
whether displaying Doppler shift, amplitude only or variance
information.
In the foregoing specification, the invention is described with
reference to specific embodiments thereof. It will, however, be
evident that various modifications and changes may be made thereto
without departing from the broad scale or spirit of the invention
as set forth in the appended claims. The specification and drawings
are, accordingly, regarded in an illustrative rather than a
restrictive sense.
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